1. Field of the Invention
The present invention relates to a technology for use in 4-wheel drive vehicles and, more specifically, is related to an anti-skid control apparatus for vehicle braking system which effectively resolves a condition which sometimes arises when the brakes of a vehicle are quickly or sharply applied, namely the slipping and locking of the vehicle wheels.
2. Background Art
In recent years it has become common for anti-skid control apparatus for vehicle braking systems to be installed in vehicles.
An anti-skid control apparatus for vehicle braking system is an apparatus to effectively resolve the condition wherein the wheels of a vehicle have skidded and locked following the application of the brake pedal by the driver.
Additionally, in the case where, (1) following application of the brake pedal, the speed of the vehicle's wheels falls below a set value (hereinafter referred to as the simulation speed) with respect to the speed of the vehicle body, which is inferred from the speed of the wheels, the anti-skid control apparatus for vehicle braking system reduces the brake pressure to each wheel, or in the case where, (2) the rate of deceleration of the wheels exceeds a set value, and slipping occurs, the anti-skid apparatus for vehicle braking system reduces the brake pressure to each of the vehicle wheels.
The technique of simultaneous control of the left and right wheels through the so-called select-low, select-high controls is known as well.
In a 4-wheel drive vehicle where the allowable rotating difference in the space between the front and rear wheels is small, when the brake pedal is applied, due to the disproportionate effect of the drive system on the front and back wheels, and in particular on a road surface having a small friction coefficient L-.mu., as shown by (1) in FIG. 5a, the speed of the front wheels may temporarily increase (a phenomena arising from the rebounding of a drive system having been activated by the brakes).
As a result, a problem arises in that the brake pressure to the front wheel increases, as is shown by (2) in FIG. 5b, and, following this and as is shown by the dashed and solid lines in FIG. 5c, a deeper slippage (wheel lock) results in the four wheels together, resulting in an instability in the vehicle.
Please note that for clarity's sake, one wheel only from each of the pair of front wheels and rear wheels is shown in FIG. 5.